1. Field of the Invention
The present invention generally relates to an optical record medium system, and more particularly to a method and apparatus for controlling record and reproduction of an optical record medium where a header region that is plural non-record regions having different phase is arranged between recordable data regions for the distinction in the shape of the data region.
2. Description of the Related Art
Generally, there is an optical record medium with freely and repeatedly recordable capability, for instance, a rewritable compact disc (CD-RW) , a rewritable digital versatile disc (DVD-RW, DVD-RAM, DVD+RW), etc.
The rewritable digital versatile disc, especially DVD-RAM has a signal track consisting of a land and groove structure. Data can be recorded on a track of the land and groove as well as a track of the land or groove or can be reproduced through the track of the land and groove as well as the track of the land or groove.
FIG. 1 is a block diagram of a record and reproduction apparatus for these optical discs.
Referring to FIG. 1, the apparatus includes an optical pickup 102. The optical pick-up 102 allows the light beam concentrated on an object lens to be placed on the signal track of an optical disc 101 according to the control of a servo control part 107, and the light beam that is reflected on a signal record face of the signal track and is then incident to be concentrated on the object lens and to be incident into an optical detector for the detection of a focus error signal and a tracking error signal. The optical detector includes a plurality of light detecting elements. An electrical signal that is proportional to the light amount obtained by each of the light detecting elements is output to a RF & servo error generating part 103.
If the optical detector, as shown in FIG. 2, consists of four optical detectors of PDA, PDB, PDC, and PDD that are divided into a specific, for example, four sectors along the signal track direction and the radial direction, the optical detector outputs to the RF & servo error generating part 103 electrical signals of a, b, c, and d that are proportional to the light amount obtained by each of the optical detectors of PDA, PDB, PDC and PDD.
The RF and servo error generating part 103 makes a combination of the electrical signals of a, b, c and d to generate an RF signal that is necessary for the data reproduction, and a tracking error signal and a focus error signal that are necessary for the servo control.
Here, the RF signal is obtained by adding all of the electrical signals of a, b, c and d (a+b+c+d) The tracking error signal can be obtained by processing a signal of (a+d)−(b+c) referred to as Read Channel 2 signal (R-ch2).
If the optical detector is divided into two sectors along the track direction, the optical detector detects the RF signal (=I1+I2) and the R-ch2 from both photo diodes I1 and I2. In other words, a+d of FIG. 2 corresponds to I1 and b+c corresponds to I2.
Then, since there is no information in an initial disc in case of the DVD-RAM 101, it is impossible to control and record the disc.
To this end, to perform the tracking control, a disc track is made in the land and groove, information is recorded along a corresponding track, and control information for sector address, random access and rotational control are additively recorded on the disc, thereby allowing the tracking control to be performed even for a vacant disc on which information signal is not recorded. The control information can be recorded at an initial position of each sector by pre-formatting the header region.
In case of DVD-RAM, the header region that is pre-formatted at the initial position of each sector consists of four header fields (header 1 field-header 4 field). The header 1 and 2 fields and the header 3 and 4 fields are crossed about the track center. FIG. 3 is one example of such a cross arrangement and shows a constitution of a header field for the first sector in one track.
The above constituted header, however, badly affects on really generating a servo error signal such as tracking error signal and focus error signal. In other words, the servo error signal read on the header region is distorted depending on the header constitution, which is followed by a difficulty in controlling the servo signal.
Accordingly, in case of DVD-RAM, there is an effort for decreasing an influence of the header by holding respective servo error signals, for instance, tracking error signal and focus error signal in order to generate servo error signal and control the generated servo error signal with stability and thereby controlling the servo.
That is, a focus sampling & holding part 104-1 of a sampling & holder part 104 samples a focus error signal (FE) and holds the sampled focus error signal at the header region, and a tracking sampling & holding part 104-2 samples a tracking error signal (TE) and holds the sampled tracking error signal at the header region, thereby allowing the light beam not to be deviate from the track center.
A selection part 104-3 selects the focus error signal and the tracking error signal which are sampled and held by the focus sampling & holding part 104-1 and the tracking sampling & holding part 104-2, respectively as a header mask signal (HDM) representing the header region is output from a header mask & L/G switching signal generating part 106, i.e., at the header region, while the selection part 104-3 selects a focus error signal and a tracking error signal that do not pass through the focus sampling & holding part 104-1 and the tracking sampling & holding part 104-2 and outputs the selected signals to an off-set control part 105 in cases other than the above circumstance, i. e., at the record region.
This means that the focus servo and the tracking servo are performed at the header region not using tracking error signal and focus error signal that are detected in real but using a holding value. Here, there are some kinds of methods for detecting the header region. The header mask & L/G switching signal generating part 106 detects this header region, generates the header mask signal (HDM) representing the header region within the detected header region, and outputs the generated header mask signal to the selection part 104-3 of the sampling & holding part 104.
Here, the header region can be detected by slicing the RF signal or R-ch2, or by generating IP1 and IP2 signals from R-ch2 and then making a combination of the IP1 and IP2 signals. That is, since the header 1 and 2 fields and the header 3 and 4 fields are crossed about the track center, IP1 and IP2 signals can be detected by slicing R-ch2 of the header region. For instance, assuming that IP1 signal is output when the track center is set to be the slice level and the R-ch2 has a level higher than the slice level and IP2 signal is output when the R-ch2 has a level lower than the slice level, phases of the IP1 and IP2 signals are changed depending on whether the present operation track is land or groove. In other words, either IP1 signal or IP2 signal can be firstly placed depending on whether the present operation track is land or groove.
Meanwhile, the tracking error signal in the land has an inversion relation to the tracking error signal in the groove. In other words, the tracking error signal detected in the land has an inversion phase relation compared with the tracking error signal detected in the groove. Thus, in order to normally follow the track in both of the land and the groove tracking error signals respectively obtained in the land and the groove have the same phase with each other.
Also, there exists a difference in a DC off-set that is basically, respectively contained in the land and the groove due to a difference in depth between the land and the groove. The DC off-set is an amount that is generated in the terms of signal due to the difference in depth between the land and the groove. Although the focus and the tracking are appropriate at the track of the land, de-focus or de-track may be generated when the focus and the tracking are identically applied to the track of the groove. In addition, when the focus and the tracking are adjusted to the track of the groove, the de-focus and the de-track can be likewise generated at the track of the land due to a difference in depth between the land and the groove.
The off-set control part 105 is provided for this reason. A focus off-set control part of the off-set control part 105 adjusts the focus error off-set that is appropriate for each of the groove and the land to perform a normal focus servo. Also, the tracking off-set control part 105-2 adjusts the tracking error off-set that is appropriate for each of the groove and the land to perform a normal tracking servo and simultaneously inverses the tracking error signal that is detected at the land.
And, the tracking off-set control part 105-2 is operated depending on switching signals of L/Gsw output from the header mask signal & L/G switching signal generating part 106: i. e., the tracking off-set control part 105-2 selects the focus error signal whose off-set is adjusted to the land and an inverted tracking error signal when the present signal track represents the land, while the tracking off-set control part 105-2 selects the focus error signal whose off-set is adjusted to the groove and the tracking error signal. The selected signal is output to the servo control part 107. Thus, the servo control part 107 performs the focus servo and the tracking servo whose off-sets are adjusted to the land through a focus/track (F/T) servo driving part 108, or performs the focus servo and the tracking servo whose off-sets are adjusted to the groove. These behaviors are determined by the L/G switching signals (L/Gsw) Here, the L/G means that the signal track is converted from the land to the groove or from the groove to the land.
That is, according to whether the present track is the land or the groove, IP1 signal or IP2 signal may precede. Thus, the header mask & L/G switching signal generating part 106 determines that the present track is the land or the groove considering which one of the land or the groove signal precedes and inverts the L/G switching signal (L/Gsw) and outputs the inverted signal to the offset control part 105.
At this time, as one method for holding the focus error signal and the tracking error signal during the header region period, there is a method for sampling and holding the focus and tracking error values of right before the header region starts. Also, the header region existing on the L/G switching is covered with header mask such that the light beams do not deviate from the track center, a focus and tracking error prior to the header region value is sampled and is held during the header region period.
However, since the sample & holder 104 is made of analog circuit, a drop occurs due to the charging and afterwards discharging of RC time delay, thereby generating a transient response. Also, since the tracking error signal of the previous track (prior to inverting) is sampled/held at the header region that exists on L/G switching, and inverted to thereby perform the tracking servo, there occurs a drawback increasing the track error.
For example, at the header region existing during the switching from the land to the groove, the tracking error signal detected at the land is sampled/held and is switched to the groove, and simultaneously the holding value is inverted to perform the tracking servo. At this time, since the land and the groove have a different DC off-set due to the difference in depth between the land and the groove, the tracking error signal is bounded by the off-set amount of the land when the land is Switched to the groove as shown in FIG. 5 and thereby the servo becomes unstable. In other words, the off-set of the land highly increases by the inverting.
Also, at the header region existing when the groove is switched to the land, the tracking error signal detected in the header region is sampled and held, and thereafter is switched to the land, and simultaneously the holding value is inverted, the tracking servo is performed. Likewise, at the header region existing when the groove is switched to the land, the track error increases by the above mentioned reason when the groove is switched to the land as shown in FIG. 6.
These problems may occur not at the L/G switching region but at the header region existing in the land track or the groove track when the error is large.
FIG. 5 is a waveform showing an example of a track error that occurs when sampling and holding the header region existing on switching from the land to the groove and FIG. 6 is a waveform showing an example of a track error that occurs when sampling and holding the header region existing on switching from the groove to the land.
Thus, when the servo becomes unstable or a header region exists within the same track or on switching from the land track to the groove track and vice verse, a value of a previous track region is sampled and held, and thereby is inverted, which causes the following problems.
First, since the header region is not detected exactly, a track sliding phenomenon may occur.
Second, a track servo becomes unstable due to a variation of a discrete track error. Especially, when the variation is serious, a slad servo becomes unstable, too.
Third, the instability of the track servo lowers the characteristics of the record and reproduction, thereby having a bad influence on the quality of the eye pattern and the jitter.